The neurotrophic properties of a nine amino acid core peptide (ADNF-9) derived from activity dependent neurotrophic factor was investigated in cell cultures produced from the rat cerebral cortex. Comparative studies of ADNF-9 action in mixed (glia plus neurons) versus glia-depleted neuronal cultures indicated that ADNF-9 can act directly on neurons, although the potency of the peptide was 10,000-fold greater in mixed cultures. Kinetic studies showed that exposure to ADNF-9 for only two hours was sufficient to produce a four day protection against the cell killing action of tetrodotoxin. Treatment with bafilomycin A1 for two hours prevented this ADNF-9-mediated neuroprotection. Antiserum to ADNF increased the number of apoptotic neurons in cerebral cortical cultures and decreased the activity of choline acetyltransferase in spinal cord cultures. ADNP, a cloned protein with shared epitopes and biological activity with ADNF, was localized in the embryonic and adult CNS on the mouse by in situ hybridization. ADNP mRNA was detected in the trophoblast and the placenta, with intense labeling in the floor plate. In adult brain, ADNP mRNA was especially intense in the olfactory bulb, thalamus, hippocampus and cerebellum. Administration of anti-ADNF to pregnant mice significantly inhibited embryonic growth and produced microcephaly. Progeny from anti-ADNF-treated mothers exhibited significant decreases in performance on an incremental DRL schedule learning paradigm when tested as adults. VIP is a secretagogue of ADNF. In the pregnant mouse, a transient increase in mRNA for VIP was found in the trophoblast at E6 and E7. VIP binding sites were abundant in the E6 trophoblast and in the embryonic neuroepithelium and decidua throughout pregnancy. VIP mRNA was not detected in the mouse embryo until E11-12. Early pregnancy factor (EPF) mRNA was detected throughout the brains of adult mice, but this greater intensity in the thalamic nuclei and cortex during pregnancy. EPF mRNA was also present in the embryonic neuroepithelium and the surrounding amniotic and trophoblastic membranes from E6 to E12. An active peptide from EPF was shown to prevent the growth-inhibitory effects of gp120, the envelope protein from the human immunodeficiency virus.